Acceleration, Speed and Velocity Acceleration is how quickly velocity changes. When the velocity of an object changes, the object is accelerating. Symbol: a Unit: m/s2 http://glencoe.mcgraw-hill.com/sites/dl/free/0078600510/161752/00035808.html

Change in velocity Initial velocity is the beginning velocity ( starts from rest= zero). Symbol: vi Unit: m/s Final velocity is the ending velocity (if the object ends at rest= zero). Symbol: vf

Speeding Up and Slowing Down When you think of acceleration, you probably think of something speeding up. However, an object that is slowing down also is accelerating. Acceleration also has direction, just as velocity does. Acceleration can be speeding up, slowing down, or changing direction

Changing Direction The speed of the horses in this carousel is constant, but the horses are accelerating because their direction is changing constantly.

Calculating Acceleration To calculate the acceleration of an object, the change in velocity is divided by the length of time interval over which the change occurred. Formula

Calculating Acceleration A ball is dropped from a cliff and has an acceleration of 9.8 m/s2. How long will it take the ball to reach a speed of 24.5 m/s? Because it started from rest, its initial speed was zero.

Graphing Acceleration Speeding up Slowing down displacement displacement time time displacement displacement time time

Motion and Position If Alice walks forward on a bus 2 meters while the bus moves forward 10 meters, How far does Alice walk according to the passengers? How far does Alice walk according to Arlo standing at the side of the road?

A reference point is needed to determine the position of an object. Motion and Position A reference point is needed to determine the position of an object. The motion of an object depends on the reference point that is chosen

Relative Motion If you are sitting in a chair reading this sentence, you are moving. You are not moving relative to your desk or your school building, but you are moving relative to the other planets in the solar system and the Sun.

Relative Motion Object with reference point speed 108,000 km/h Moon speed around the Earth 3,683 km/h 2,288 miles/h Earth speed around the Sun 108,000 km/h 66,600 miles/h The Sun speed around the center of the galaxy 828,000 km/h 514,000 miles/h

Longer distances are measured in kilometers (km). Distance is: how far an object has moved. Symbol: d Unit m Longer distances are measured in kilometers (km).

Displacement Displacement is the distance and direction of an object's final position compared to its initial position. Symbol: Δx Unit m The key here is DIRECTION so an object’s path does not matter

Distance versus displacement The distance around a track once is 400 meters (1/4 mile) *What is the runner’s displacement? *What about the Earth around the Sun? *How does a car measure distance?

Speed is how fast an object moves Symbol: s Unit: m/s

Velocity is how fast an object moves and the direction it moves Symbol: v Unit: m/s

Velocity *Because velocity depends on direction as well as speed, the velocity of an object can change even if the speed of the object remains constant. *The speed of this car might be constant, but its velocity is not constant because the direction of motion is always changing.